scholarly journals Large-conductance calcium-activated potassium current modulates excitability in isolated canine intracardiac neurons

2013 ◽  
Vol 304 (3) ◽  
pp. C280-C286 ◽  
Author(s):  
Guillermo J. Pérez ◽  
Mayurika Desai ◽  
Seth Anderson ◽  
Fabiana S. Scornik
Keyword(s):  
Membrane Potential ◽  
Calcium Release ◽  
Single Channel ◽  
Calcium Influx ◽  
Ryanodine Receptors ◽  
Bk Channels ◽  
Release Mechanism ◽  
Dependent Manner ◽  
Whole Cell ◽  
Intracardiac Neurons

We studied principal neurons from canine intracardiac (IC) ganglia to determine whether large-conductance calcium-activated potassium (BK) channels play a role in their excitability. We performed whole cell recordings in voltage- and current-clamp modes to measure ion currents and changes in membrane potential from isolated canine IC neurons. Whole cell currents from these neurons showed fast- and slow-activated outward components. Both current components decreased in the absence of calcium and following 1–2 mM tetraethylammonium (TEA) or paxilline. These results suggest that BK channels underlie these current components. Single-channel analysis showed that BK channels from IC neurons do not inactivate in a time-dependent manner, suggesting that the dynamic of the decay of the fast current component is akin to that of intracellular calcium. Immunohistochemical studies showed that BK channels and type 2 ryanodine receptors are coexpressed in IC principal neurons. We tested whether BK current activation in these neurons occurred via a calcium-induced calcium release mechanism. We found that the outward currents of these neurons were not affected by the calcium depletion of intracellular stores with 10 mM caffeine and 10 μM cyclopiazonic acid. Thus, in canine intracardiac neurons, BK currents are directly activated by calcium influx. Membrane potential changes elicited by long (400 ms) current injections showed a tonic firing response that was decreased by TEA or paxilline. These data strongly suggest that the BK current present in canine intracardiac neurons regulates action potential activity and could increase these neurons excitability.

Abstract 327: Attenuated Beta-Adrenergic Response in the Tric-a Knock Out Mice

Circulation ◽  
2018 ◽  
Vol 138 (Suppl_2) ◽  
Author(s):  
Yuichi Toyama ◽  
Manabu Yonekura ◽  
Chong Han ◽  
Hirofumi Tomita ◽  
Hiroshi Takeshima ◽  
...  
Keyword(s):  
Heart Rate ◽  
Action Potential ◽  
Sympathetic Nerve ◽  
Calcium Release ◽  
Calcium Influx ◽  
Ryanodine Receptors ◽  
Low Frequency ◽  
Beta Adrenergic ◽  
Knock Out ◽  
Nerve Regulation

Trimeric intracellular cation (TRIC) channels are expressed on the surface of sarcoplasmic reticulum (SR) and regulate calcium release from ryanodine receptors (RyRs). In a previous study, Tric-a knock out (KO) mice showed diminished calcium release from RyRs following increased calcium-influx via L-type calcium channels, which results in enhanced vascular resistance and non-dipper type hypertension. Decreased activation of RyR1 by PKA in skeletal myocytes in Tric-a KO mice is also known. However, physiological importance of TRIC channels on cardiac rhythm formation and its importance on the sympathetic nerve regulation are still obscure. Therefore, we aimed to clarify the effects of Tric-a ablation on cardiac pace making using Tric-a KO mice. We measured systolic blood pressure (SBP) with tail-cuff method, ECG and spontaneous action potential with microelectrode in the Tric-a KO and wild type (WT) mice. Isoproterenol or propranolol was used for sympathetic nerve manipulation. Furthermore, we evaluated heart rate variability (HRV). Tric-a KO mice tended to show limited responses to isoproterenol (0.3 mg/kg) than the WT mice (-27 ± 6 and -32 ± 6 mmHg, n = 10, p =0.70), and to propranolol (4 ± 6 and 13 ± 7 mmHg, n = 5~6, p =0.48). In ECG analysis, ablation of Tric-a gene resulted in significantly decreased heart rate changes to isoproterenol (23 ± 6 and 99 ± 15 bpm, Tric-a KO and WT mice, respectively, n = 9~10, p <0.001). Response to propranolol was also significantly decreased in the Tric-a KO mice (-28 ± 20 and -122 ± 14 bpm, Tric-a KO and WT mice, respectively, n = 9~10, p <0.001). In the action potential recordings, Tric-a KO mice showed significantly decreased sinus rate changes to 1 microM isoproterenol (35 ± 9 and 71 ± 10 bpm, Tric-a KO and WT mice, respectively, n = 6~8, p <0.05). In HRV analysis, low-frequency/high-frequency (LF/HF) ratio tended to be lower in the Tric-a KO mice than the WT mice under the administration of isoproterenol (0.22 ± 0.31 and 0.65 ± 0.16 bpm, Tric-a KO and WT mice, respectively, n = 9~11, p =0.16), suggesting lower sympathetic nerve tonus in the Tric-a KO mice. In conclusion, our data indicates that Tric-a KO mice showed attenuated responses to beta-adrenergic stimulus, which indicates involvement of TRIC-A channels in sympathetic nerve regulation.

Development of Transient Outward Currents Coupled With Ca2+-Induced Ca2+ Release Mediates Oscillatory Membrane Potential in Ascidian Muscle Cells

2004 ◽  
Vol 92 (2) ◽  
pp. 1056-1066 ◽  
Author(s):  
Koichi Nakajo ◽  
Yasushi Okamura
Keyword(s):  
Membrane Potential ◽  
Voltage Clamp ◽  
Muscle Cell ◽  
Single Channel ◽  
Muscle Cells ◽  
Developmental Expression ◽  
Dependent Manner ◽  
Membrane Excitability ◽  
Halocynthia Roretzi ◽  
Outward Currents

Isolated ascidian Halocynthia roretzi blastomeres of the muscle lineage exhibit muscle cell-like excitability on differentiation despite the arrest of cell cleavage early in development. This characteristic provides a unique opportunity to track changes in ion channel expression during muscle cell differentiation. Here, we show that the intrinsic membrane property of ascidian cleavage-arrested muscle-type cells becomes oscillatory by expressing transient outward currents ( Ito) activated by Ca2+-induced Ca2+ release (CICR) in a maturation-dependent manner. In current-clamp mode, most day 4 (72 h after fertilization) cleavage-arrested muscle cells exhibited an oscillatory membrane potential of –20 mV at 15 Hz, whereas most day 3 (48 h after fertilization) cells exhibited a spiking pattern. In voltage-clamp mode, the day 4 cells exhibited prominent transient outward currents that were not present in day 3 cells. Ito was abolished by the application of 10 mM caffeine, implying that CICR was involved in Ito activation. Ito was based on K+ efflux and sensitive to tetraethylammonium and some Ca2+-activated K+ channel inhibitors. We found a 60-pS single channel conductance that was activated by local Ca2+ release in ascidian muscle cell. Voltage-clamp recording with an oscillatory waveform as a command pulse showed that CICR-activated K+ currents were activated during the falling phase of the membrane potential oscillation. These results suggest that developmental expression of CICR-activated K+ current plays a role in the maturation of larval locomotion by modifying the intrinsic membrane excitability of muscle cells.

Opening of large-conductance calcium-activated potassium channels by the substituted benzimidazolone NS004

1994 ◽  
Vol 71 (5) ◽  
pp. 1873-1882 ◽  
Author(s):  
M. C. McKay ◽  
S. I. Dworetzky ◽  
N. A. Meanwell ◽  
S. P. Olesen ◽  
P. H. Reinhart ◽  
...  
Keyword(s):  
Rat Brain ◽  
Lipid Bilayers ◽  
Single Channel ◽  
Outward Current ◽  
Calcium Sensitivity ◽  
Bk Channels ◽  
Gh3 Cells ◽  
Xenopus Laevis Oocytes ◽  
Planar Lipid Bilayers ◽  
Whole Cell

1. We used electrophysiological techniques to examine the effects of 5-trifluoromethyl-1-(5-chloro-2-hydroxyphenyl)-1,3-dihydro-2H-benzimidaz ole- 2-one (NS004) on large-conductance calcium-activated potassium (BK) channels. 2. We used recordings from excised membrane patches (cell-attached and inside-out single-channel configurations) and whole-cell patch-clamp recordings to examine the effects of NS004 on single BK channels and whole-cell outward currents, respectively, in rat GH3 clonal pituitary tumor cells. We also tested NS004 on voltage-clamped BK channels isolated from rat brain plasma membrane preparations and reconstituted into planar lipid bilayers. Finally, we used two-electrode voltage-clamp techniques to study the effects of NS004 on currents expressed in Xenopus laevis oocytes by the recently described Slo BK clone from Drosophila. 3. In GH3 cells and in Xenopus oocytes expressing the Slo gene product NS004 produced an increase in an iberiotoxin- or tetraethylammonium-sensitive whole-cell outward current, respectively. NS004 produced a significant increase in the activity of single GH3 cell BK channels and rat brain BK channels reconstituted into planar lipid bilayers. In both systems this was characterized by an increase in channel mean open time, a decrease in interburst interval, and an apparent increase in channel voltage/calcium sensitivity. 4. These data indicate that NS004 could be useful for investigating the biophysical and molecular properties of BK channels and for determining the functional consequences of the opening of BK channels.

scholarly journals Calcium homeostasis in a local/global whole cell model of permeabilized ventricular myocytes with a Langevin description of stochastic calcium release

2015 ◽  
Vol 308 (5) ◽  
pp. H510-H523 ◽  
Author(s):  
Xiao Wang ◽  
Seth H. Weinberg ◽  
Yan Hao ◽  
Eric A. Sobie ◽  
Gregory D. Smith
Keyword(s):  
Calcium Release ◽  
Ventricular Myocytes ◽  
Cell Model ◽  
Ryanodine Receptors ◽  
Planck Equation ◽  
Linear Increase ◽  
Langevin Equations ◽  
Cell Models ◽  
Whole Cell ◽  
Alternative Approach

Population density approaches to modeling local control of Ca2+-induced Ca2+ release in cardiac myocytes can be used to construct minimal whole cell models that accurately represent heterogeneous local Ca2+ signals. Unfortunately, the computational complexity of such “local/global” whole cell models scales with the number of Ca2+ release unit (CaRU) states, which is a rapidly increasing function of the number of ryanodine receptors (RyRs) per CaRU. Here we present an alternative approach based on a Langevin description of the collective gating of RyRs coupled by local Ca2+ concentration ([Ca2+]). The computational efficiency of this approach no longer depends on the number of RyRs per CaRU. When the RyR model is minimal, Langevin equations may be replaced by a single Fokker-Planck equation, yielding an extremely compact and efficient local/global whole cell model that reproduces and helps interpret recent experiments that investigate Ca2+ homeostasis in permeabilized ventricular myocytes. Our calculations show that elevated myoplasmic [Ca2+] promotes elevated network sarcoplasmic reticulum (SR) [Ca2+] via SR Ca2+-ATPase-mediated Ca2+ uptake. However, elevated myoplasmic [Ca2+] may also activate RyRs and promote stochastic SR Ca2+ release, which can in turn decrease SR [Ca2+]. Increasing myoplasmic [Ca2+] results in an exponential increase in spark-mediated release and a linear increase in nonspark-mediated release, consistent with recent experiments. The model exhibits two steady-state release fluxes for the same network SR [Ca2+] depending on whether myoplasmic [Ca2+] is low or high. In the later case, spontaneous release decreases SR [Ca2+] in a manner that maintains robust Ca2+ sparks.

scholarly journals Calcium-Induced Calcium Release in Smooth Muscle

2000 ◽  
Vol 115 (5) ◽  
pp. 653-662 ◽  
Author(s):  
M.L. Collier ◽  
G. Ji ◽  
Y.-X. Wang ◽  
M.I. Kotlikoff
Keyword(s):  
Smooth Muscle ◽  
Calcium Release ◽  
Striated Muscle ◽  
Single Channel ◽  
Ryanodine Receptors ◽  
Cytosolic Calcium ◽  
Heart Cells ◽  
Tight Coupling ◽  
Calcium Induced Calcium Release ◽  
Ca2 Channels

Calcium-induced calcium release (CICR) has been observed in cardiac myocytes as elementary calcium release events (calcium sparks) associated with the opening of L-type Ca2+ channels. In heart cells, a tight coupling between the gating of single L-type Ca2+ channels and ryanodine receptors (RYRs) underlies calcium release. Here we demonstrate that L-type Ca2+ channels activate RYRs to produce CICR in smooth muscle cells in the form of Ca2+ sparks and propagated Ca2+ waves. However, unlike CICR in cardiac muscle, RYR channel opening is not tightly linked to the gating of L-type Ca2+ channels. L-type Ca2+ channels can open without triggering Ca2+ sparks and triggered Ca2+ sparks are often observed after channel closure. CICR is a function of the net flux of Ca2+ ions into the cytosol, rather than the single channel amplitude of L-type Ca2+ channels. Moreover, unlike CICR in striated muscle, calcium release is completely eliminated by cytosolic calcium buffering. Thus, L-type Ca2+ channels are loosely coupled to RYR through an increase in global [Ca2+] due to an increase in the effective distance between L-type Ca2+ channels and RYR, resulting in an uncoupling of the obligate relationship that exists in striated muscle between the action potential and calcium release.

Modulation of type-1 Ins(1,4,5)P3 receptor channels by the FK506-binding protein, FKBP12

2002 ◽  
Vol 361 (2) ◽  
pp. 401-407 ◽  
Author(s):  
Sheila L. DARGAN ◽  
Edward J. A. LEA ◽  
Alan P. DAWSON
Keyword(s):  
Lipid Bilayers ◽  
Calcium Release ◽  
Single Channel ◽  
Binding Protein ◽  
Ryanodine Receptors ◽  
Fk506 Binding Protein ◽  
Single Channel Activity ◽  
And Function ◽  
First Time

FK506-binding protein (FKBP12) is highly expressed in neuronal tissue, where it is proposed to localize calcineurin to intracellular calcium-release channels, ryanodine receptors and Ins(1,4,5)P3 receptors (InsP3Rs). The effects of FKBP12 on ryanodine receptors have been well characterized but the nature and function of binding of FKBP12 to InsP3R is more controversial, with evidence for and against a tight interaction between these two proteins. To investigate this, we incorporated purified type-1 InsP3R from rat cerebellum into planar lipid bilayers to monitor the effects of exogenous recombinant FKBP12 on single-channel activity, using K+ as the current carrier. Here we report for the first time that FKBP12 causes a substantial change in single-channel properties of the type-1 InsP3R, specifically to increase the amount of time the channel spends in a fully open state. In the presence of ATP, FKBP12 can also induce co-ordinated gating with neighbouring receptors. The effects of FKBP12 were reversed by FK506. We also present data showing that rapamycin, at sub-optimal concentrations of Ins(2,4,5)P3, decreases the rate of calcium release from cerebellar microsomes. These results provide evidence for a direct functional interaction between FKBP12 and the type-1 InsP3R.

scholarly journals Functional Coupling of β3-Adrenoceptors and Large Conductance Calcium-Activated Potassium Channels in Human Uterine Myocytes

2005 ◽  
Vol 90 (10) ◽  
pp. 5786-5796 ◽  
Author(s):  
Helen C. Doheny ◽  
Caoimhe M. Lynch ◽  
Terry J. Smith ◽  
John J. Morrison
Keyword(s):  
Single Channel ◽  
State Probability ◽  
Human Myometrium ◽  
Bkca Channel ◽  
Functional Coupling ◽  
Dependent Manner ◽  
Whole Cell ◽  
Single Channel Recordings ◽  
Presence And Absence

Context: β3-Adrenoreceptor modulation in human myometrium during pregnancy is linked functionally to myometrial inhibition. Maxi-K+ channels (BKCa) play a significant role in modulating cell membrane potential and excitability. Objective: This study was designed to investigate the potential involvement of BKCa channel function in the response of human myometrium to β3-adrenoceptor activation. Design: Single and whole-cell electrophysiological BKCa channel recordings from freshly dispersed myocytes were obtained in the presence and absence of BRL37344, a specific β3-adrenoreceptor agonist. The in vitro effects of BRL37344 on isolated myometrial contractions, in the presence and absence of the specific BKCa channel blocker, iberiotoxin (IbTX), were investigated. Setting: The study was carried out at the Clinical Science Institute. Patients or Other Participants: Myometrial biopsies were obtained at elective cesarean delivery. Intervention: No intervention was applied. Main Outcome Measures: Open state probability of single channel recordings, whole cell currents, and myometrial contractile activity were measured. Results: Single-channel recordings identified the BKCa channel as a target of BRL37344. BRL37344 significantly increased the open state probability of this channel in a concentration-dependent manner (control 0.031 ± 0.004; 50 μm BRL37344 0.073 ± 0.005 (P &lt; 0.001); and 100 μm BRL37344 0.101 ± 0.005 (P &lt; 0.001). This effect was completely blocked after preincubation of the cells with 1 μm bupranolol, a nonspecific β-adrenoreceptor blocker, or 100 nm SR59230a, a specific β3-adrenoreceptor antagonist. In addition, BRL37344 increased whole-cell currents over a range of membrane potentials, and this effect was reversed by 100 nm IbTX. In vitro isometric tension studies demonstrated that BRL37344 exerted a significant concentration-dependent relaxant effect on human myometrial tissue (P &lt; 0.05), and preincubation of these strips with IbTX attenuated this effect on both spontaneous and oxytocin-induced contractions (44.44 and 57.84% at 10−5m, respectively). Conclusions: These findings outline that activation of the BKCa channel may explain the potent uterorelaxant effect of β3-adrenoreceptor agonists.

scholarly journals Mechanism of inhibitory action of TMB-8 [8-(NN-diethylamino)octyl-3,4,5-trimethoxybenzoate] on aldosterone secretion in adrenal glomerulosa cells

1985 ◽  
Vol 232 (1) ◽  
pp. 87-92 ◽  
Author(s):  
I Kojima ◽  
K Kojima ◽  
H Rasmussen
Keyword(s):  
Protein Kinase C ◽  
Angiotensin Ii ◽  
Protein Kinase ◽  
Calcium Release ◽  
Calcium Influx ◽  
Inhibitory Effect ◽  
Dependent Manner ◽  
Aldosterone Secretion ◽  
Kinase C ◽  
Glomerulosa Cells

The mechanism of 8-(NN-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) action was evaluated in isolated adrenal glomerulosa cells. TMB-8 inhibits both angiotensin II- and K+-stimulated aldosterone secretion in a dose-dependent manner. The ID50 for angiotensin II- and K+-stimulated aldosterone secretion is 46 and 28 microM, respectively. In spite of the fact that 100 microM-TMB-8 inhibits angiotensin II-stimulated aldosterone secretion almost completely, TMB-8 (100 microM) does not inhibit angiotensin II-induced 45Ca2+ efflux from prelabelled cells nor does it affect inositol 1,4,5-trisphosphate-induced calcium release from non-mitochondrial pool(s) in saponin-permeabilized cells. TMB-8 has no inhibitory effect on A23187-induced aldosterone secretion, but 12-O-tetradecanoylphorbol 13-acetate-induced aldosterone secretion is completely abolished. TMB-8 effectively inhibits both angiotensin II- and K+-induced increases in calcium influx but has no effect on A23187-induced calcium influx. TMB-8 inhibits the activity of protein kinase C dose-dependently. These results indicate that TMB-8 inhibits aldosterone secretion without inhibiting mobilization of calcium from an intracellular pool. The inhibitory effect of TMB-8 is due largely to an inhibition of plasma membrane calcium influx, but this drug also inhibits the activity of protein kinase C directly.

scholarly journals Single calcium channel behavior in native skeletal muscle.

1995 ◽  
Vol 105 (2) ◽  
pp. 227-247 ◽  
Author(s):  
R T Dirksen ◽  
K G Beam
Keyword(s):  
Skeletal Muscle ◽  
Calcium Channels ◽  
Single Channel ◽  
Bay K 8644 ◽  
Dependent Manner ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Whole Cell ◽  
Macroscopic Properties ◽  
Voltage Dependent

The purpose of this study was to use whole-cell and cell-attached patches of cultured skeletal muscle myotubes to study the macroscopic and unitary behavior of voltage-dependent calcium channels under similar conditions. With 110 mM BaCl2 as the charge carrier, two types of calcium channels with markedly different single-channel and macroscopic properties were found. One class was DHP-insensitive, had a single-channel conductance of approximately 9 pS, yielded ensembles that displayed an activation threshold near -40 mV, and activated and inactivated rapidly in a voltage-dependent manner (T current). The second class could only be well resolved in the presence of the DHP agonist Bay K 8644 (5 microM) and had a single-channel conductance of approximately 14 pS (L current). The 14-pS channel produced ensembles exhibiting a threshold of approximately -10 mV that activated slowly (tau act approximately 20 ms) and displayed little inactivation. Moreover, the DHP antagonist, (+)-PN 200-110 (10 microM), greatly increased the percentage of null sweeps seen with the 14-pS channel. The open probability versus voltage relationship of the 14-pS channel was fitted by a Boltzmann distribution with a VP0.5 = 6.2 mV and kp = 5.3 mV. L current recorded from whole-cell experiments in the presence of 110 mM BaCl2 + 5 microM Bay K 8644 displayed similar time- and voltage-dependent properties as ensembles of the 14-pS channel. Thus, these data are the first comparison under similar conditions of the single-channel and macroscopic properties of T current and L current in native skeletal muscle, and identify the 9- and 14-pS channels as the single-channel correlates of T current and L current, respectively.

scholarly journals Membrane potential and Ca2+ concentration dependence on pressure and vasoactive agents in arterial smooth muscle: A model

2015 ◽  
Vol 146 (1) ◽  
pp. 79-96 ◽  
Author(s):  
Arthur Karlin
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Cerebral Arteries ◽  
Ryanodine Receptors ◽  
Vessel Diameter ◽  
Bk Channels ◽  
Epoxyeicosatrienoic Acid ◽  
Arterial Smooth Muscle ◽  
Cl Channels ◽  
Protein Components

Arterial smooth muscle (SM) cells respond autonomously to changes in intravascular pressure, adjusting tension to maintain vessel diameter. The values of membrane potential (Vm) and sarcoplasmic Ca2+ concentration (Cain) within minutes of a change in pressure are the results of two opposing pathways, both of which use Ca2+ as a signal. This works because the two Ca2+-signaling pathways are confined to distinct microdomains in which the Ca2+ concentrations needed to activate key channels are transiently higher than Cain. A mathematical model of an isolated arterial SM cell is presented that incorporates the two types of microdomains. The first type consists of junctions between cisternae of the peripheral sarcoplasmic reticulum (SR), containing ryanodine receptors (RyRs), and the sarcolemma, containing voltage- and Ca2+-activated K+ (BK) channels. These junctional microdomains promote hyperpolarization, reduced Cain, and relaxation. The second type is postulated to form around stretch-activated nonspecific cation channels and neighboring Ca2+-activated Cl− channels, and promotes the opposite (depolarization, increased Cain, and contraction). The model includes three additional compartments: the sarcoplasm, the central SR lumen, and the peripheral SR lumen. It incorporates 37 protein components. In addition to pressure, the model accommodates inputs of α- and β-adrenergic agonists, ATP, 11,12-epoxyeicosatrienoic acid, and nitric oxide (NO). The parameters of the equations were adjusted to obtain a close fit to reported Vm and Cain as functions of pressure, which have been determined in cerebral arteries. The simulations were insensitive to ±10% changes in most of the parameters. The model also simulated the effects of inhibiting RyR, BK, or voltage-activated Ca2+ channels on Vm and Cain. Deletion of BK β1 subunits is known to increase arterial–SM tension. In the model, deletion of β1 raised Cain at all pressures, and these increases were reversed by NO.

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